Compositions for release coating application can be in the form of emulsion (water-based), solvent-based or solventless (free of solvent). Solventless silicone release coating compositions have some important advantages over solvent-based and emulsion coating compositions:                Fewer environmental, health, safety, and regulatory concerns        No solvent recovery equipment required        Contain no carrier that must be driven off, so line speeds can be faster        Less likely to damage films.        
Conventionally, a solventless (SL) type silicone release coating has fast cure but base polymers in coating bath have to be low viscosity to meet the multiple rolls coating process requirement. The low viscosity limits the degrees of polymerization of polyorganosiloxane for a base polymer. It may be difficult to provide slippery surface to the cured coating and low release force for adhesive majorly due to tight crosslinking density. To overcome such a technical problem, the prior art has proposed several solutions.
For example, WO 2008084747 A2 (Patent Reference 1, incorporated herein for reference) discloses a solventless, cured release coating-forming organopolysiloxane composition, comprising:    (A) 100 parts of an organopolysiloxane fluid having a branched structure and comprising            (i) the siloxane unit represented by the formula SiO4/2,        (ii) the siloxane unit represented by the general formula R2SiO2/2, and        (iii) the siloxane unit represented by the general formula RaR2SiO1/2;            (B) 0.5 to 15 parts of a diorganopolysiloxane with the average structural formula RaRc2SiO(RbRcSiO2/2)n1(Rc2SiO2/2)n2SiRc2Ra;    (C) a prescribed quantity of an organohydrogenpolysiloxane; and    (D) a hydrosilylation reaction catalyst.
Also, a sheet-form substrate that has a cured coating from this solventless, cured release coating-forming organopolysiloxane composition is provided.
The diorganopolysiloxane (B) contains alkenyl groups. It is said [0029] that the alkenyl content must be kept very low, especially maximum 0.1 mole % of the silicone-bonded organic groups being alkenyl (it may well be that the word “mole” means in fact “weight”). According to the examples, the vinyl content in the component (B) of Patent reference 1 is 0.02 weight %.
Component (B) of patent reference 1 must have a viscosity at 25 C of at least 100,000 mPa s and preferably at least 1,000,000 mPa s (see [0030]).
Comparative example 3 of WO 2008084747 A2 discloses the following composition: 100 parts of the dimethylvinylsiloxy-end blocked dimethylpolysiloxane shown by the following average structural formula (viscosity=400 mPa·s, calculated vi % (vinyl %)=0.62 wt %),

1.0 part of (B<1>) dimethylsiloxane diphenylsiloxane copolymer having molecular chain terminals end blocked by a dimethylvinylsiloxy group and a trimethylsiloxy group (diphenylsiloxane unit content=5 mol %, viscosity=50,000 mPa·$), 2.0 parts of (C) methylhydrogenpolysiloxane endblocked at both molecular chain terminals by trimethylsiloxy groups (viscosity=20 mPa·s, silicon-bonded hydrogen content=1.6 weight %), and 0.30 parts of (E) 1-ethynyl-1-cyclohexanol were mixed to homogeneity; into this mixture was admixed a (D) chloroplatinic acid-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex (platinum metal content=0.60 wt %) in a quantity sufficient to give 100 ppm platinum (also named platinum) metal, thus yielding a solventless, cured release coating-forming organopolysiloxane composition (viscosity=400 mPa s); the dynamic coefficient of friction and the peel resistance value were measured on the obtained composition; these results are shown in Table 4. WO 2008084747 A2 indicates that the technical intention thereof is “bleed-out” effect of slippery additive having high viscosity on the surface of the cured layer. The additive may create a loose structure by light end-linked with vulcanized network with crosslinker or entanglement of long polymeric chains.
For example, JP 61159480 A (Patent Reference 2, incorporated herein for reference) discloses a silicone composition for release paper which is characterized by comprising:    1) Organopolysiloxane having at least two or more vinyl groups in a molecule, at least one or more vinyl groups bonding on side-chain position, the content of vinyl group within 0.5 to 10.0 mol % and viscosity at 25° C. of 50 to 10,000 mPa s 100 weight parts;    2) Organopolysiloxane having smaller content of vinyl group than said organopolysiloxane and viscosity at 25° C. of at least 100,000 mPa s 0.5 to 30.0 weight parts;    3) Organohydrogenpolysiloxane having at least two silicon-bonded hydrogen in a molecule 0.5 to 60.0 weight parts; and    4) Catalytic quantity of Platinum or Platinum compounds.
JP 61159480 A provides a release coating characterized by low- or non-reactive gum migration (bleed-out) (breed-out) onto the surface of cured coating layer providing good slipperiness. JP 61159480 A indicates that its object is to obtain a silicone composition which imports excellent slipperiness to material to be treated, by blending two organopolysiloxanes, an organohydrogenpolysiloxane and a platinum catalyst.
For example, WO 2005059039 A2 (Patent Reference 3, incorporated herein for reference) discloses a thermal addition curable solventless silicone release composition having a reduced coefficient of friction and improved slip characteristics. The invention is also directed to a method using alpha-olefins with reactive polyorganosiloxane for producing a thermal addition curable solventless silicone release composition on a substrate by applying the thermal addition curable solventless release composition of the invention to a substrate and curing the coating on the substrate using heat. The invention is further directed to a thermal addition curable solventless silicone release coated article having a reduced coefficient of friction and improved slip characteristics.
For example, US 20110287267 A1 (Patent Reference 4, incorporated herein for reference) discloses a solventless cured release coating-forming organopolysiloxane composition having a viscosity at 25° C. of 50 to 2,000 mPa·s, comprising (A) 100 weight parts of an alkenyl-functional diorganopolysiloxane that has a viscosity of 25 to 1,000 mPa·s; (B) 0.5 to 15 weight parts of a diorganopolysiloxane that has a viscosity of at least 10,000 mPa·s and that has an aliphatically unsaturated group content of no more than 0.1 mol %; (C) 0.5 to 5 weight parts of a branched organopolysiloxane that has more than one SiO4/2 unit and that is a polymer product provided by an equilibration polymerization between a branched organosiloxane oligomer represented by the average siloxane unit formula (1) (SiO4/2)(RaRb2SiO1/2)x(1) and a diorganosiloxane oligomer; (D) a specific amount of an organohydrogenpolysiloxane that has a viscosity of 1 to 1,000 mPa·s; and (E) a hydrosilylation reaction catalyst in a catalytic quantity.
For example, U.S. Pat. No. 6,569,914 B2 (Patent Reference 5, incorporated herein for reference) discloses low solvent and solvent-free silicone release coatings, which may be prepared with varying COF (COEFFICIENT OF FRICTION) levels by incorporating a very high molecular weight, substantially non-reactive organopolysiloxane into a conventional curable release coating. By supplying the COF additive in the form of a relatively low viscosity master batch, adjustment of COF may be made by the coating applicator. Very low COF values can be obtained from tin-free, solvent-free coating systems, while at the same time, the coatings have very low extractables.
For example, U.S. Pat. No. 4,123,604 A (Patent Reference 6, incorporated herein for reference) discloses a novel and improved coating composition and an improved process for coating substrates. The compositions are essentially solventless and when cured give highly abrasion resistant coatings, non-blocking characteristics, fast cure and a general overall aesthetic appearance. An example of coating a substrate is the coating of paper products to give release from adhesives.
For example, U.S. Pat. No. 4,870,149 A (Patent Reference 7, incorporated herein for reference) discloses a solvent-free releasing silicone composition for rendering surfaces non-adherent which gives a cured film having desirable slip factor, toughness, and high-speed peel characteristics without sacrificing its inherent merits such as curability, uniformity in peel resistance, and the residual adhesive strength employs a diorganovinylpolysiloxane having trivinylsilyloxy as one end group and either a vinyldimethylsilyl or trimethylsilyl group as the other end group.
For example, U.S. Pat. No. 5,432,006 A (Patent Reference 8, incorporated herein for reference) discloses curable, solventless, liquid polyorganosiloxane compositions, which provide release coatings that exhibit a slippery feel. The composition comprises (a) a first polydiorganosiloxane terminated by silyl groups having one reactive group; (b) a second polydiorganosiloxane terminated by silyl groups having one reactive group, the reactive group of (a) being the same or different from the reactive group of (b), said reactive groups of (a) and (b) being reactive with one another to form a covalent bond; (c) a polydiorganosiloxane having three or more reactive groups that are reactive with either the reactive group of (a) or the reactive group of (b) or both to form a covalent bond; and (d) a catalyst for effecting the reaction of the reactive groups of (a), (b), and (c) to form covalent bonds. When coated on a substrate and cured, the composition provides release liners for pressure-sensitive adhesive tapes and pressure-sensitive adhesive transfer tapes.
However, the above Patent References 1-8 fail to well solve the above technical problem. Particularly, both Patent Reference 1 and Patent Reference 2 disclose using organopolysiloxane having a higher viscosity than 100,000 mPa s. Furthermore, in these Patent References, the viscosity of below 100,000 mPa s results in poor slipperiness of obtained cured coating layer for insufficient bleed-out effect and much adhesive residue thereof. From practical viewpoint of these inventions, the viscosity of 100,000 mPa s seems to be insufficient. Preferred one should be polysiloxane having viscosity of 1,000,000 mPa s or more. For example, both Patent References disclose to use extra high molecular weight (gum state) organopolysiloxanes having at least 1,000,000 mPa s in all practical examples. Therefore, both Patent Reference 1 and Patent Reference 2 need polymer with higher viscosity for its specific technical effect. For example, as seen from the paragraph [0006] and paragraphs [0026]-[0030] of Patent Reference 1, the component (B), polysiloxane having viscosity of at least 100,000 mPa s, functions to improve the releasability of the cured coating with respect to tacky substances and also functions to provide the cured coating with slipperiness. That is to say, though the component (B) has light linkage with cure network, it shall have free polymer chains bleed-out on the surface of cured coating layer and provide good slipperiness on it. Additionally, without vi-group in pendant position in defined range, the gum state organopolysiloxanes tends to easily extract from the cured body, if end-group reaction is not working well. However, obviously, neither Patent Reference 1, Patent Reference 2 nor Patent Reference 5 can easily provide a limited release coating composition keeping suitable low viscosity for multiple roll-coater, while possessing excellent properties.
Therefore, there still exists a need in the art for obtaining a release coating composition keeping suitable low viscosity for multiple roll-coater, while possessing excellent properties including high-speed cure with low amount of catalyst, cured layer with low migration, slippery & good smooth touch of the coating surface, good anchorage to the substrate, and low release force to sticky adhesives.